Method of working metal



Sept. 2, 1930. H, Dow ET AL I METHOD oF WORKING METAL Filed July 30. 1926 Jcg, 4.

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Patented Sept. 2, -1930 UNITED STATES PATENT oFFicE HERBERT H. DOW AND `IOHN E. HOY, OF MIDLAND, MICHIGAN, ASSIGNORS TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN j METHOD OF WORKING METAL Application led. July 30, 1926. Serial No. 125,913'.

The present improvements have more particular regard to the working of articles cast from light metals, such as, for example, aluminum and magnesium and alloys thereof, in which either of the metals just named forms the predominant constituent. An alu` minum alloy of the type in question is at present more or less extensivelymarketed under the name of Duralium, and a corresponding magnesium alloy is similarly marketed under the name of Dowmetal, the latter comprising approximately 90 per cent of magnesium, with aluminum and other metals alloyed therewith. 1

The object of the invention is to improve the physical structure of such cast articles, and particularly where the articles are cast in tubular form, either open or closed, and still more specifically Where the article is in the form of a piston which is of general hollow cylindrical form closed at one end, as is.

well known.

It has been discovered that by .subjecting the metal of such an article adjacent its working'surface to plastic deformation in a direction parallel with the axis of the article where the latter is of vsuch tubular or cylindrical form, not only is the inherent strength measurably increased, but a surface is produced having a superior wearing quality, as is particularly important in the case of a piston. At the same time that the metal adjacent the outer lateral surface is thus plastically deformed,vin the case of such piston it is advantageous to carry such plastic deformation across the end or head of the piston, radially inwardly from the periphery of the head, with the result that the latter is similarly strengthenedy and a surface produced having or capable of receiving a superior finish. j

To the accomplishment of the foregoing and related ends, the invention would consist of the steps and means hereinafter fully described andparticularly set forth in the claim, the following description and annexed drawing villustrating but several of the various ways in which the invention may be carried out. l

I In said annexed drawing Fig; 1 is a central vertical section through an apparatus or mechanism designed for carmodified form of mechanism for thus working metal.

As previously indicated, the article shown as being4 worked in both Figs. l and 2 is a" piston casting (l), this being shown as of conventional type, i. e. as consisting of a head portion (2) and a depending cylindrical skirt portion (3). Projecting inwardly from opposite sides of the latter are two similar bosses (4), through which extend the aligned openings (5) designed to receive the wrist pin in the finally assembled condition of the piston. Such bosses are also shown as joined to the head of the piston by means of Webs or ribs (6). v

As actually cast, the outer lateral surface of the piston is not strictly cylindrical, but tapers slightly upwardly and outwardly as clearly shown'in Fig. 1. The outer edge (7) of the head is also preferably beveled off as shown.

In the form of the mechanism illustrated in Figs. l and 2, an outer die member (10) is provided of general hollow4 cylindrical form, being made of steel and with the walls of such thickness or so supported as to render said membercapable of withstanding the strains to which it is subjected in the operation to be described. -The upper portion of the opening or bore in said die member, i. e. down to the line L -a, is of outwardly tapering conformation so as exactly tov Iitthe casting upon insertion of the latter. On the contrary, the lower portion of the opening sponding with the minimum diameter of the upper tapered portion of the bore 1n die (10) j casting, i. e. the diameter of the lower en'dof the latter.

Prior to its insertion in the die member, the casting is mounted upon a collapsible .die of vfamiliar construction, such die being made of plural hardened steel parts (l1- 11) which ma be assembled within the castin and there eld in place by means of a tapere pin (12), as will be readily understood. Such core-parts ('11) `are supported on a base plate (13) through a central opening in which the pin' (12) projects, the latter being provided With a threaded extension (14), with a ,nut (15) thereon that is adapted to bear against a U-shaped block (16) that seats upon the underside of such plate.

In the operation of the foregoing mechanism, the casting (1) with the collapsible die parts (11) inserted therein and held in place by means of pin (12) is dropped into the so as to occupy the position shown in Fig. v1. Thereupon a pressure actuated plunger (17) is brou ht down upon the head of the casting an the latter forced downwardly entirely through the die. This plunger, it will be noted, is of a diameter corresponding with that of the lower portion of the die and furthermore has a, central depression (18) formed in its underface.

As a result of the operation just described, the metal of the casting adjacent the outer cylindrical surface thereof is forced upwardly and at the same time that in the head is forced regularly-inwardly, and the excess accumulated in the hollow space (18) in the underface of the plunger (17), such flow of the metal in the casting being diagrammatically illustrated by the arrows in Fig. 3.

The same .effect in the Way of plastic deformationof the metal in a casting of the general shape under consideration maybe produced, at leastlto la certain extent, without actually forcing the casting through the die,

. but as shown in Fig. 4 the casting, supported as before by means ofl a collapsible core, may be placed'in a die (20),' the interior of which 1s tapered to conform with the exterior shape of the casting. In this case, however, thelower end of the die is closed by the plate (21) upon which the collapsible core members (22) seat, and instead of a plunger applying continuous pressureto the casting, a hammer (23) of corresponding shape to 'that of plunger (17) is caused to strike repeatedly upon the head of the casting. In place of operating the vhammer (23) so as to subject the casting to repeated blows, one continuous steady blow may be employed by means thereof, as in a bulldozer or equivalent heavy duty press.

The results as before will be to cause more or less of a longitudinal iowV of metal upwardly adjacent the outer cylindrical surface of the casting and radially inwardly across its toplsurface, t-he surplus metal accumulating as before in a hollow space (24) will still be of general tapered form exteriorly instead of being finished to desired cylindrical form as in the case of the first described mechanism. It will accordingly be necessary to turn or machine down the casting in the second case to its proper cylindrical shape.

Whichever form of mechanism is employed, the die as well as the collapsible core will be preliminarily heated to a temperature approximately the upper limit to which the casting may be heated without melting the eutectic present as will ordinarily be the case if such casting is composed of an alloy of various metals with either aluminum or magnesium or both. Such casting will also be preliminarily heated to substantially the same temperature. varyfrom 600,o to 850 F. for magnesium base alloys and may go to 900 F. for Duralium, in which aluminum isthe predominant constituent.

In Working piston castings in the manner hereinbefore described, it has been found that the tensile strength may be increased as much as 50 per cent., and that at the same time the exterior surface both of the lateral walls and the top of the piston have a superior iinish imparted thereto. It will be understood, of course, that the central protuberance of metal on the piston head caused by the ow of excess metal into the hollows (18 or 24) as This temperature may the case may be, will ordinarily be cut off in the finished article.

Other modes .of applying the principle of our invention may be employed instead of the one explained, change being made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be elnployed.

We thereforelparticularly point out and distinctly claim as our invention z- In a method of working cast pistons, or

similarly 'shaped articles of light metal, the step which consists in subjecting the metal of the latter adjacent the outer cylindrical surface thereof to plastic deformation in a longitudinal direction', and at the same time causing the metal to flow radially inwardly,

, across the top ofthe article.

26th day of July, 1926. HERBERT H. DOW. JOHN E. HOY.

.Signed by us this iso 

